The present invention relates to thermoplastic urethane elastomeric alloys containing as a first component at least one polyurethane elastomer and as a second composition at least one thermoplastic elastomer that is not within the definition of the first component.
Silicone has been used medically in various applications, e.g., pumps, but has been found to have a number of undesirable properties such as poor abrasion resistance which results in particles flaking off and, in the case of medical applications, accumulating in one or another organ in the body, low tensile strength, poor flex fatigue, and poor barrier properties. Styrene-butadiene elastomers have been evaluated as substitutes for silicone and are inexpensive and processable but lack excellent tear resistance and tensile strength. There is a need for materials that overcome the disadvantages of silicone.
U.S. Pat. No. 4,608,418 to Czerwinski et al. teaches hot melt urethane compositions formed from a mixture of one or more polyisocyanates, one or more hydroxyl terminated polyols, one or more chain extenders and one or more plasticizers. A hot melt composition generally is one applied in the molten state, at temperatures of about 250.degree.-450.degree. F. (121.1.degree.-232.2.degree. C.), and having a viscosity in that condition (Brookfield viscometer) of less than about 50,000 cps, preferably less than about 25,000 cps. When cooled to room temperature, such compositions are solids that are elastomeric in nature. These compositions are formed by heating the reactants at temperatures of at least about 330.degree. F. (165.6.degree. C.), preferably at about 350.degree. F. to about 450.degree. F. (176.7.degree.-232.2.degree. C.) for 2 or 3 hours. The compositions of this patent have been found to be an excellent first material for use in the present invention. The disclosure of the 4,608,418 patent is hereby incorporated by reference.